1. Field of the Invention
An aspect of the present invention relates to a nailing machine.
2. Description of the Related Art
Spring-driven nailing machines pushing up a plunger, which is urged by a nailing spring, against the urging force of the nailing spring to a top dead center, accelerating the plunger by opening the nailing spring, and driving a nail into a target member with the plunger have already been produced. In the nailing machines, the labor for pushing up the plunger is reduced by pushing the plunger by the use of the motor built in the housing. Specifically, as described in JP-9-295283-A, plural rotating gears coupled to the motor with a reduction gear therebetween are disposed opposite each other and a driving pin fixed to a position departing from the rotation centers of the rotating gears is made to engage with an engaging protrusion formed in the plunger. The plunger is pushed up by a predetermined stroke by the use of the driving pin.
A nailing spring used in the conventional nailing machines is urged at the position of a top dead center by a motor, etc. to accumulate elastic energy and is opened at the time of hitting to move toward a bottom dead center. When an end of the nailing spring reaches the position of the bottom dead center, the end of the nailing spring starts being compressed, and the other end of the nailing spring moves to the bottom dead center, whereby the elastic energy is accumulated in the nailing spring at the position of the bottom dead center again. When the nailing spring is compressed to some extent, the nailing spring moves toward the top dead center with the accumulated elastic energy and the other end of the nailing spring reaches the position of the top dead center, whereby the elastic energy is accumulated in the nailing spring again.
By repeating this operation at the positions of the top dead center and the bottom dead center, the nailing spring is attenuated to return to the before-nailing state. Accordingly, the ends of the nailing spring always reach the position of the top dead center and the position of the bottom dead center and thus both ends of the nailing spring essentially suffer from the greatest impact and thus are expanded and compressed. Therefore, the nailing spring might be deteriorated from the ends. As a countermeasure, it can be considered that the strength of the nailing spring is enhanced by enlarging the nailing spring. However, in this case, the nailing machine increases in size, the spring constant is enhanced, and the hitting power becomes too strong, thereby damaging the workability. An object of the invention is to provide a nailing machine having a small size and a long lifetime.